1. Technical Field
The present invention relates to an IPM (Interior Permanent Magnet) type of synchronous machine, and in particular, to an IPM type of synchronous machine that generates magnet torque and reluctance torque.
2. Related Art
There has been known a synchronous machine that generates magnet torque and reluctance torque (hereinafter, such a synchronous machine will now be referred to as a reluctance-parallel-use magnet synchronous machine). One of the most familiar reluctance-parallel-use magnet synchronous machines is an IPM (Interior Permanent Magnet) type of synchronous motor.
The reluctance torque Tr is obtained when there is provided a difference between q-axis inductance Lq and d-axis inductance Ld. Because the magnetic resistance of a permanent magnet is higher, the q-axis inductance Lq is usually made larger in strength than the d-axis inductance Ld. However, this is not the only possible structure. The d-axis inductance Ld may be made larger in strength than the q-axis inductance Lq.
In the normally used structure where the intensity of the q-axis inductance Lq is larger than that of the d-axis inductance Ld, magnetic salient poles are arranged at the q-axis positions and permanent magnets are arranged at the d-axis positions in order to increase the intensity of the q-axis inductance Lq.
The magnetic salient poles can be realized by a structure where the outer surface of a rotor made of soft magnetism material is made spatially salient in the radially outward at every electrical angle π. In addition, the magnetic salient poles can also be realized by embedding flux barriers within a cylindrical stator made of soft magnetism material. Examples of the reluctance-parallel-use magnet synchronous machine are shown for example in Japanese Patent Application Laid-open Publications No. 2000-60038, 2001-339922, 2002-44920 and 2003-324875. It is widely known that the reluctance-parallel-use magnet synchronous machine has the capability of generating reluctance torque Tr as well as magnet torque Tm, whereby torque, i.e., output per body weight is larger.
However, the conventional reluctance-parallel-use magnet IS synchronous machine is not sufficient in that, for increasing the output torque, the machine is obliged to use a larger amount of rare-earth magnet, which is very expensive.